Frequency divider



Jan. 16, 1951 w. BROWN ET AL FREQUENCY DIVIDER Filed March 4, 1947 KEYERINVENTORS W/LL/AM BROWN EARL H. SCHOE/VFELD ATTORNEY Patented Jan. 16,1951 FREQUENCY DIVIDER William Brown, Far Rockaway, and Earl H.Schoenfeld, Mamaroneck, N. Y., assignors to Radio Corporation ofAmerica, a corporation of Delaware Application March 4, 1947, Serial No.732,286 8 Claims. (01. zso-sei This invention relates to frequencydividers, and more particularly to a simplified and improved frequencydivider.

An object of the invention is to provide a stable frequency divideremploying a single tube and a delay line in circuit therewith, andcapable of dividing by 2, 4, 6, etc., depending upon the constants ofthe delay line.

Another object of the invention is to provide a frequency divider whichcan be keyed to start or stop within a fractional period of a cycle ofthe frequency to be divided, and which provides uniform output impulsesduring the entire keying on" interval without variation of eitheramplitude or phase of these impulses during the on interval.

Another object of the invention is to provide a stable frequency dividerwhich may be keyed without the introduction of transients.

Another object of the present invention is to provide a frequencydivider which can be keyed and satisfies the following requirements: 1.A negligible leakage of the input energy to the output terminals. 2.Provide output impulses whose wave forms are substantial replicas ofthese portions of the input wave forms which have a given polarity, and3. Provide, during a keying interval, a predetermined number ofuniformly spaced impulses whose wave forms and peak amplitudes areidentical.

Another object is to provide a frequency divider whose output pulseshave an amplitude substantially greater than that of the input Wavewhose frequency is to be divided.

A more detailed description of the invention folows in conjunction witha drawing, wherein:

Fig. 1 illustrates a simplified form of a frequency divider embodyingthe principles of the present invention; and

Fig. 2 is a series of curves given in explanation of the operation ofthe frequency divider of the invention.

Referring to Fig. 1, there is shown a frequency divider comprising apentagrid vacuum tube 10 whose plate is connected by way of lead I! l toone end of artificial line TL whose other end is connected through ablocking condenser I2 and lead 9 to the third grid of the tube. Line TLis a constant K filter which is composed of a multiplicity of seriesinductances and shunt capacitances. Obviously, the invention is notlimited to this particular form of artificial line, since other types oflines includin a real line can be employed to provide the desired delayfor pulses traveling thereover. That end of line TL which is connectedto the blocking condenser I2 is terminated by a resistor l3 whose valueis equal to the surge impedance of the line. This resistor 13 isconnected to a suitable source of plate polariznected to each other andthrough lead 23 to a cycles applied to input leads 20, 20.

with a potential which is positive relative to the cathode. A radiofrequency bypass condenser 55 is connected between ground and the 13+supply as shown. One side of the line TL is connected to ground, and thecathode of the tube It is also grounded.

The input wave of fundamental frequency which is to be divided issupplied through input leads 20, in turn, connected to the primarywinding of a transformer TR whose secondary winding is connected betweenthe first grid and the cathode of tube Ill. The primary and secondarywindings of transformer TR form parts of tuned circuits which resonateat the frequency of the in put wave. Suitable grid leak resistors 29 and22 are provided between the first and third grids respectively, and thecathode. The fifth grid of tube iii, known as the suppressor grid, isconnected directly to the cathode. The second and fourth grids, known asthe screen grids, are directly consuitable source'of keying waves 26.This keyer 24 is adapted to supply rectangular wave pulses of positivepolarity to the screen grids of tube Hi at a repetition rate which islow compared to the frequency of the output pulses and whose pulse rateis synchronized with a sub-multiple of the frequency of the input waves.Output pulses of divided frequency may be obtained across terminals M.

The operation of the system of Fig. 1 may be better understood byreferring to the curves l 2, and 3 of Fig. 2. Let it be assumed, forexample, that the energy of the driving source of the fundamentalfrequency is a sin wave of 360 kilo- Curve I of Fig. 2 shows such a sinewave which has zero amplitude at times A', B, C, D, E, F, etc. Assumingfor the present that there is a positive voltage on the screen grid oftube Ill, the. positive half-cycles of the sine wave of curve 1 causeplate current to flow through the tube l!) in the absence of negativevoltage on its third grid. However, when plate current flows on thefirst positive half-cycle, a voltage drop equal to the surge impedanceof the line TL multiplied by the plate current flowing through tube ii!is impressed on the input of the line TL.. This voltage drop constitutesan impulse which is shown in curve 2 between times A. and B, and thisimpulse travels down the line TL toward the resistor i3, arriving at theterminating resistor is as shown between the times C and D of curve 3.This impulse in curve 3 is of negative polarity with respect to groundand is impressed upon the third grid of The time constants of the lineTL are so chosen that the negative impulse impressed on the third gridoc-- curs during the time when the immediately sucing potential B+through .a filter or decoupling. o. ceeding positivehalf-cycle of curvel is applied to resistor 34. In this way, the plate is supplied ff the'first grid of the tube. This negative impulse which is applied to thethird grid of tube is of such magnitude as to prevent a flow of platecurrent in tube I 0 during this occurrence. It will thus be seen from aninspection of the curves of Fig. 2 that the tube It] draws plate currentonly during alternate positive half-cycles of the applied input Wave.

Although the system of Fig. 1 has been described with particularreference to a: frequency halver, it will be obvious that the constantsof the filter TL may be selected so as to delay the negative pulsesapplied to the third grid by periods of 2, 3, or any integral number ofcomplete cycles of the input wave. Thus, if for instance the delay timeof the filter TL is equal to two cycles of the input wave, both thefirst and. seo-- plate current to flow in the vacuum tube [0 anda pairof negative pulses corresponding to these plate current pulses will beapplied to the input of the filter TL- This pair of pulses beingsubjected to the two cycle delay time of the new filter TL will now beimpressed on the third grid of tube l0 via condenser [2. during thethird and fourth positive half-cycles of the input wave and prevent thepassage of plate current at those particular times. Thus, plate currentwill flow for two half-cycles, be cut-off for two half-cycles, againflow for two half-cycles, etc. In thismanner the output energy will havea component whose frequency is A; of that of the input wave. In the samemanner, if the filter were designed to have a delay time equal to threecycles of the input wave the output of the system would consist ofgroups of three pulses followed by a quiescent period equal to threecycles etc., thus giving an output component at /3 the frequency of theinput wave.

In describing the operation of the invention in connection with thecurves of Fig. 2, it was assumed that a positive voltage existed on thescreen grids of the pentagrid tube. This positive voltage, however, neednot be permanently connected to the screen grids but may be supplied asa keying wave by means of keyer 24, as shown. If this keyer wereomitted, the screen grids may be bypassed to the cathode through a radiofrequency bypass condenser. The keyer 24 supplies rectangular or squarewave pulses of positive polarity to the screen grids of tube H] at a lowfrequency relative to the frequency of the input wave. As anillustration only, the pulse rate of these keying pulses may be 25cycles per second. In order for the frequency divider of the inventionto be'keyed so as to start or stop within a fractional period of a cycleof the frequency to be divided and provide uniform output pulses duringthe entire. keying on interval without variation Of either amplitude orphase of these output impulses during the on interval, the positivepolarity keying pulses should be applied to the screen grids during theintervals between times B and C, or D and E, or F and G of Fig. 2. Itwill be seen that these intervals B to C, D to E; and F to G, are theintervals during which the negative half-cycles of the input wave occur.To achieve this result it is important to synchronize the keyer pulserate with a sub-multiple frequency of the input wave to be divided. Inthis way the frequency divider of the invention will be ready to operate'on the succeeding positive half-cycle of the input wave which positivehalfcycle of the input wave follows the negative halfcycle during. whichthe keying pulses starts.

The keying wave may, if desired, have a duration equal to ten or morecomplete cycles of the input wave energy, and all of the output pulsesduring that keying interval will occur at a sub-multiple rate. withrespect to the input frequency and will be uniformly spaced and have thesame peak amplitude and the same wave form.

An advantage of the system of the present invention is that the outputpulses obtainable across terminals M are a sub-multiple of the frequencyof the input wave and may have an amplitude which is greater than theamplitude of the input wave.

It should be understood that the invention is not limited to thespecific circuit arrangement illustrated and described inasmuch asequivalent. circuit details may replace those illustrated withoutdeparting from the spirit and scope of the invention. As anillustration, the divided fre-- quency may be taken from the input orplatethe output end of the line TL may be connected to ground throughresistor l3. Other equivalent details will be obvious to anyone skilledin theart.

What is claimed is:

l. A frequency divider comprising a pentagrid vacuum tube having acathode, five grids and a plate, a direct connection between thesuppressorgrid and the cathode of said tube, means for applyingunidirectional potential to said plate,

means for applying input waves of fundamentalfrequency between the firstgrid and said cathode, and a delay line, a connection between one. endof said delay line and said plate, a connection including a seriallyarranged capacitor between the other end of said delay line and thethird grid of said tube, a terminating resistor connected to one end ofsaid line, said delay line having such constants and being soconstructedand arranged that the voltage wave traveling thereover when said tubedraws cur-' rent is delayed a predetermined integral humber of cycles ofthe input Wave before being applied as a negative pulse to the thirdgrid.

2. A frequency divider comprising a pentagrid vacuum tube having acathode, five grids and a plate, a direct connection between the suppressor grid and the cathode of said tube, a source of input waves offundamental frequency coupled between the first grid and said cathode,and a delay line having one end coupled to said plate and its other endcoupled to the third grid of said tube, terminating resistor connectedto one end of said line, said delay line having such constants that thevoltage wave traveling there-- over when said tube draws current isdelayed a predetermined integral number of cycles of the input wavebefore being applied to the third grid,-

h shunt capacitances, said series inductances bethe terminal inductanceat one end of the line to said plate, a, connection from the otherterminal inductance at the other end of the line to the third grid ofsaid tube, a connection from the other side of the line to said cathode,means for applying polarizing potential to said plate, means forapplying waves whose frequency is to be divided coupled between saidcathode and the first grid of said tube, and output terminals forextracting waves of sub-multiple frequency coupled to said cathode andthe line, said line having such constants between its ends and being soconstructed and arranged that the voltage wave traveling thereover whensaid tube draws plate current is delayed a predetermined number ofcycles of the input wave before being applied to said third grid, thatend of said line which is connected to said third grid being soterminated that the voltage Wave which travels over the line is appliedto the third grid as a negative pulse with such magnitude as to preventsaid tube from drawing plate current during the interval in which it isbeing applied to the third grid.

4. A frequency divider comprising a pentagrid vacuum tube having acathode, five grids and a plate, an artificial line composed ofaplurality of sections of series inductances and shunt capacitances, aconnection from the terminal inductance at one end of the line to saidplate, a

connection from the other terminal inductance at the other end of theline to the third grid of said tube, a connection from one side of theline to said cathode, a source of plate polarizing potential connectedto said plate, a source of waves whose frequency is to be dividedcoupled between said cathode and the first grid of said tube, and outputterminals for extracting waves of submultiple frequency coupled to saidcathode and the line, said line having such constants between its endsthat the voltage wave traveling thereover when said tube draws currentis delayed a predetermined number of cycles of the input wave beforebeing applied to said third grid, that end of said line which isconnected to said third grid being so terminated that the voltage wavewhich travels over the line is applied to the third grid in such senseand magnitude as to prevent said tube from drawing current during theinterval in which it is being applied to the third grid, and a source ofkeying waves coupled ,to the screen grid of said tube, said last sourcebeing synchronized with a sub-multiple of the frequency of the inputwaves and supplying pulses of positive polarity to said screen gridrelative to said cathode.

5. A frequency divider comprising a pentagrid vacuum tube havingcathode, five grids and a plate, a direct connection between thesuppressor grid and the cathode of said tube, a source of input waves offundamental frequency coupled between the first grid and said cathode,and a delay line having one end coupled to said plate and its other endcoupled to xthe third grid of said tube, said delay line having suchconstants that the voltage wave traveling thereover,

when said tube draws current is delayed a predetermined integral numberof cycles of the input Wave before being applied to the third grid, anda source of keying waves coupled to the second and fourth grids of saidtube, said last source supplying pulses of positive polarity to saidsecond and fourth grids at a repetition rate considerably lower than thefrequency of the input waves, that end of the line which is connected 6to said third grid being so terminated that the voltage wave whichtravels over the line is applied to the third grid in such sense andmagnitude as to prevent said tube from drawing plate current during theinterval in which it is applied to the third grid.

6. A frequency divider comprising a multigrid tube having a cathode, apair of grids and a plate, means for applying an operating potential tosaid plate, means for applying input waves of fundamental frequencybetween one of said grids and said cathode, and a delay line, aconnection between one end of said delay line and said plate, aconnection between the other end of said delay line and the other gridof said tube, said last connection consisting of a lead in series with acondenser, said delay line having such constants and being soconstructed and arranged that the voltage wave traveling thereover whensaid tube draws current is delayed a predetermined integral number ofcycles of the input wave before being applied as a negative pulse tosaid other grid.

'7. A frequency divider comprising a multigrid tube having a cathode, apair of grids and a plate, means for applying an operating potential tosaid plate, means for applying input waves of fundamental frequencybetween one of said grids and said cathode, and a delay line having oneend coupled to said plate and its other end coupled to the other grid ofsaid tube, the coupling between the last end of the delay line and saidother grid being capable of passing a pulsating current, a connectionfrom one side of said delay line to said cathode, said delay line havingsuch constants and being so constructed and arranged that the voltagewave traveling thereover when said tube draws current is delayed apredetermined integral number of cycles of the input wave before beingapplied as a negative pulse to said other grid, and output terminalscoupled to said cathode and the line for extracting waves of asub-multiple frequency.

8. A frequency divider comprising a pentagrid vacuum tube having acathode, five grids and a plate, a direct connection between thesuppressor grid and the cathode of said tube, means for applying anoperating potential to said plate, means for applying input waves offundamental frequency coupled between the first grid and said cathode,and a delay line coupled between said plate and the third grid of saidtube, said delay line having such constants that the voltage wavetraveling thereover when said tube draws current is delayed apredetermined integral number of cycles of the input wave before beingapplied to the third grid, and means for applying keying waves coupledto the second and fourth grids of said tube, said last means supplyingpulses of positive polarity to said second and fourth grids at a,repetition rate considerably lower than the frequency of th input waves.

WILLIAM BROWN. EARL H. SCHOENFELD.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,212,173 Wheeler Aug. 20, 1940FOREIGN: PATENTS Number Countiiy Date 479,935 Great Britain Feb. 14,1938

